ProjectSummary Duchennemusculardystrophy(DMD)isachronic,musclewastingdiseaseforwhichthereisnocure. StrategiestoreduceDMDpathologyincludedeliveryoftherapeuticmoleculestodystrophicmusclealthough thatapproachcanbelimitedbyundesirableoff-targeteffects.Forexample,leukemiainhibitoryfactor(LIF) improvesregenerationofdystrophicmuscle,butsystemicdeliveryofLIFcanhavenegativeeffectsonother tissues.Weproposetotestwhethergenetically-modifiedmacrophagescanbeusedtodeliveraLIFto dystrophicmuscle,specificallyatsitesandtimeswhenthepathologyisactive.Thisisaccomplishedbyusing theCD11bpromoterinmacrophagestodrivetheexpressionofaLIFtransgene.Becausedystrophicmuscle experiencesextensiveinfiltrationbymacrophagesduringpeakpathology,expressionofthetransgenewillbe targetedtoaffectedtissueonlyduringactivepathology.Asinflammationsubsides,expressionofthe CD11b/LIFtransgenewillbeintrinsicallydownregulated.Thus,oursystemallowsforthedeliveryofa therapeuticmoleculeinamannerthatisresponsivetothelocation,time,andmagnitudeofthedystrophic pathology.Inourinvestigation,wewilladdressthefollowingaims: Aim1:TestwhetherthesuppressedexpressionofprofibroticgenescausedbytheCD11b/LIFtransgene reducesmusclefibrosisandimprovesmusclefunction.Wewillassayforreductionsofmusclefibrosiscaused byexpressionoftheCD11b/LIFtransgeneinmacrophages,usingthemdxmousemodelofDMD.Wewillalso testwhethertransgeneexpressionimprovesrespiratoryfunction,musclestrengthandlongevityofmdxmice. Aim2:TestwhetherCD11b/LIFexpressioninmacrophagesmodifiesinflammatorycellphenotypeor interactionswithprofibroticcellsindystrophicmuscle.BecauseLIFhasthecapacitytomodifythe inflammatoryresponseandtissuefibrosis,wewilltestwhetherexpressionoftheCD11b/LIFtransgeneby macrophagesaffectsmacrophagephenotypeindystrophicmuscleoraffectsthefunction,fateorphenotypeof cellsthatcanpromotemusclefibrosis(fibro/adipogenicprogenitorcells). Aim3:TestwhetherCD11b/LIFtransgeneexpressioninmacrophagesmodifiesmuscleprogenitorcell activationormusclegrowthinmusculardystrophy.BecauseLIFhasthecapacitytoinfluencetheproliferation anddifferentiationofmuscleprogenitorcells,wewilltestwhetherexpressionoftheCD11b/LIFtransgeneby macrophagesinfluencesmyogenesisandmusclegrowthindystrophicmice. Weanticipatethatthesefindingswillestablishthefeasibilityofusingmacrophagesasvectorstodeliver therapeuticmoleculestodystrophicmuscle.Thefindingswillalsoberelevanttootherdiseasesinwhich inflammationisaprominentfeatureofthepathology.